Reduction in the band gap of anodic TiO2 nanotube arrays by H2 plasma treatment

Influence of the hydrogen (H2) plasma treatment on the anodic titanium dioxide (TiO2) nanotubes physical properties was studied. The Titanium substrates were anodized in an ethylene-glycol-based electrolyte solution containing 0.3 wt% ammonium fluoride (NH4F) and 3 vol% deionized (DI) water at a potential of 50 V for 1 h at room temperature. The TiO2 nanotubes arrays hold a great potential as the electrode materials for high-performance electrochemical applications. However, TiO2 nanotubes poor electronic conductivity limits their applications. Here, TiO2 nanotubes were treated with H2 plasma to improve the optical properties of the TiO2 nanotubes. The morphology, crystal structure, and optical band gap of the anodic TiO2 nanotubes were investigated. The morphology of the TiO2 nanotubes was studied by using field-emission scanning electron microscopy (FESEM). The roughness of the treated TiO2 nanotubes walls were enhanced compared to non-treated TiO2 nanotubes and also diameter of the H2 plasma treated nanotubes decreased. UV-Vis diffuse reflectance spectroscopy (DRS) and Photoluminescence (PL) measurements revealed that the H2 plasma treated TiO2 nanotubes have slightly lower band gap energy compare to the non-treated TiO2 nanotubes.